Modern information networks having optical interconnects utilize variable fiber optic attenuators. For example, in wave division multiplex optical networks having increased wavelength content and greater functionalities, optical communication channels may be added, dropped, and/or rerouted to any node of the network. As a result of this flexibility, the network is more complex from an optical content point of view. It is important to carefully monitor the optical power and individual wavelengths channeled as a result. Otherwise, high error rates may occur during propagation through communication channels having optical amplifiers (add-drop modules, multiplexers/demultiplexers, and other optical signal condition components). Consequently, inexpensive, reliable devices to adjust the power level of the applicable signals for higher accuracy and higher repeatability are needed.
In general, optical communication systems include several optical fiber-coupled devices (e.g., light sources, photodetectors, switches, attenuators, amplifiers, and filters). In the optical communications systems, the optical fiber-coupled devices transmit optical signals. Some optical signals that are transmitted in the optical communications systems have varying wavelengths or frequencies. The optical signals' different wavelengths transmit digital or analog data.
Several optical communication systems are lossy, i.e., the optical fibers used therein scatter or absorb portions of the optical signals transmitted therealong (about 0.1–0.2 dB/km). The power associated with the optical signals is reduced when portions of the optical signals transmitted on the optical fibers are scattered or absorbed. Positioning amplifiers in the optical communication system compensates for power reductions attributable to the optical fibers. By utilizing optical amplifiers, the power of the optical signals transmitted along the optical fibers increases.
Power variations between the different wavelengths of the optical signals may occur after the optical signals propagating along the optical fiber experience multiple cycles of power losses followed by amplification. If uncorrected, these power variations may cause adjacent wavelengths to interfere with each other, resulting in transmission errors.
When using fiber optic systems, specific control of optical signal levels entering various system components is often required. In general, optical attenuators are used to control the power variations between the different optical signal wavelengths in optical communication systems. For example, one method of controlling the optical signal levels is to use an attenuator. An adjustable attenuator allows the desired level of attenuation to be set and remain stable with time, temperature, etc. Some optical attenuators control the power variations between the different optical signal wavelengths by reflecting portions of specified optical signal wavelengths provided thereto.
Many optical attenuators include a plate attached to a substrate with torsional members, e.g., rods, springs. The plate is coated with a reflective material. By applying a torque to the torsional members, the plate is moveable relative to the substrate. The movement of the plate attenuates optical signals provided thereto by reflecting portions thereof away from the transmission path of the optical communication system.
One problem with optical attenuators that include reflective plates relates to their insertion loss. Optical attenuators, in an “off” state, typically reflect optical signals with near zero attenuation. Near zero attenuation in the “off” state requires that the reflective plates have very flat surfaces. Reflective plates with very flat surfaces are difficult to fabricate.
Also, near zero attenuation in the “off” state requires that the plane of the reflective plate be positioned parallel to the substrate. However, for a torsional plate structure, the torsional members are fragile such that the equilibrium rotation of the reflective plate potentially drifts after each “on/off” cycle. Such drifting of the reflective plate affects its position plate relative to the substrate.
Controlling the optical signal levels entering various system components is important to prevent transmission errors. This is especially true in short distance runs, where more loss of the signal is needed to prevent transmission errors.
Thus, optical attenuators continue to be sought.